8" balls! Wow, that sound huge! But fear not -- the official site indicates that the balls are 8" in circumference, not an 8" diameter. That would be pretty close to the size of a tennis ball -- nominally, a tennis ball has a circumference of ~8.26"

Did you get a sense of the speed ranges for this device? Will it work for a relatively small area (short distance feed)? I noticed that they also have a cheaper machine that uses smaller balls. It holds 26 balls that are 5.125 inches around. Smaller ball might be a more challenging target.

The point is to use real tennis ball for a realistic feel. I checked, and tennis balls work with this machine. In fact the balls they use have almost the exact same size and weight as a tennis ball.

As for speed range, it is ajustable. According to customer reviews, it goes from 25 mph to 60 mph, and can land the ball up to 30 feet away. Which is more than enough to practice my feel on volleys, and ok for a large enough basement.

A much better deal than the Tennis Twist (at 229$ and 15 mph balls) in my opinion.